1. Field of the Invention
The present invention relates to a solid-state image pickup device which performs A/D conversion on pixel signals generated in a pixel array part formed of a plurality of photoelectric conversion elements and outputs the obtained digital pixel signals, and more particularly, to a solid-state image pickup device including improved A/D converters for pixel signals, a signal processing method for such a solid-state image pickup device, and an electronic apparatus or electronic equipment including such a solid-state image pickup device. The term “electronic apparatus or electronic equipment” indicates, for example, a digital camera, a mobile telephone with a camera, or a personal computer, and the term “solid-state image pickup device” indicates an image pickup chip for a CCD image pickup device or an amplification type image pickup device (CMOS sensor), or an electronic device module in which an image pickup chip is integrated with a lens or another chip for incorporation into electronic equipment.
2. Description of the Related Art
In a related-art solid-state image pickup device which picks up an image of a subject and outputs a digital image signal, an analog image signal acquired from a photoelectric conversion element needs to be converted into a digital signal by an A/D converter provided at a predetermined position in a transmission path.
Therefore, there are various methods such as a method of converting pixel signals into digital signals in a pixel array part by means of A/D converters each provided for a plurality of pixels within the pixel array part, a method which uses A/D converters provided in a signal processing part for performing various kinds of signal processing on pixel signals transmitted from a pixel array part, and converts the pixel signals into digital signals before or after the various kinds of signal processing, and a method of converting an analog video signal into a digital video signal by means of A/D converters provided at the output stage of the analog video signal finished by a signal processing part.
The method using A/D converters provided within a pixel array part is disadvantageous when a greater number of pixels are to be arranged within the pixel array part, because the construction of each pixel becomes complicated.
The method using A/D converters provided at the output stage of a video signal is disadvantageous in terms of power consumption or the like because a video signal needs to be A/D-converted serially at a high speed and all processes such as signal processing need to be performed in an analog manner.
From these points of view, the most useful method is the method of converting an analog signal into a digital signal by means of A/D converters provided in a signal processing part near a pixel array part and then finishing a video signal through digital processing.
In a construction which reads pixel signals from a two-dimensional pixel array part into a signal processing part, the pixel lines or pixel columns of the two-dimensional pixel array part are sequentially selected by the operation of a vertical scanning circuit or a horizontal scanning circuit which is generally provided in a side portion of the two-dimensional pixel array part, and pixel signals are transferred to the signal processing part in units of pixel lines or pixel columns.
A construction which reads pixel signals in units of pixel lines will be described below by way of example.
In this construction, a signal processing part is disposed along the last line of the two-dimensional pixel array part, and signal processing circuits are provided for the respective pixel columns of the signal processing part (one set of signal processing circuits may also be provided per a group of pixel columns).
Each of the signal processing circuits sequentially acquires pixel signals from each one of the pixel columns on the basis of selection of a pixel line by the vertical scanning circuit, and performs predetermined signal processing on these pixel signals.
Incidentally, even in the case where signal processing is performed in units of pixel lines, essentially the same operation is performed.
As the signal processing in each of the signal processing parts, it is general to perform, for example, amplification and CDS (correlated double sampling) processing on various pixel signals. There may be a case where current-voltage conversion or the like is also included.
In this signal processing part, A/D converters are respectively provided to correspond to pixel columns or pixel lines of the two-dimensional pixel array part, whereby digital pixel signals can be obtained by means of a comparatively simple and inexpensive construction by performing A/D conversion on pixel signals for each of the pixel columns or the pixel lines. In addition, since rear-stage processing can be performed with digital processing, this construction can contribute to a reduction in power consumption or the like.